#23 100 Rows, Four Hours, One Request

Three numbers decide whether an abap2UI5 app feels fast, and none of them is in the app's code. They are worth knowing before the first table is bound.

100 rows. Every UI5 JSON model exposes at most 100 items to a list binding by default. Bind a table with 300 entries and the first 100 render — the rest are silently dropped, with no error anywhere. It is a UI5 setting, not a framework one, and it is raised per view from ABAP:

    client->follow_up_action( val   = client->cs_event-set_size_limit
                              t_arg = VALUE #( ( `1000` )
                                               ( client->cs_view-main ) ) ).

Raising it is the fix for a table of a thousand rows. It is not the fix for a table of fifty thousand: every bound row travels to the browser with the response, and back to the database with the draft. A screen that needs that many pages in ABAP — a SELECT with UP TO, a growing table, a filter bar — the way a selection screen always did.

Four hours. The serialized instance from #9 lives in z2ui5_t_01 until it expires, four hours by default. A user who comes back after lunch continues where they were; one who comes back tomorrow starts fresh. The number is draft_exp_time_in_hours in the user exit, and the table is the one place in the framework that grows — it is cleaned up on its own schedule, and a system with many users and long-running screens sizes it like any other table.

One request. Every click is one HTTP roundtrip plus one read and one write of the draft. The cost of a click is therefore the size of the instance and the size of the model, and the two are the same attributes. An app that carries a catalogue of ten thousand rows in an attribute pays for it on every click, in either section. An app that re-reads what it needs pays a SELECT, which the database was built for.

What a click costs: the instance to the database, the model to the browser.

The rule that follows is the same as in a dynpro program with global variables: keep in the instance what the screen shows, and nothing that can be read again.

Small instance, bounded model, one request per click. Everything else the system already does well.

Happy ABAPing! 🦖🦕🦣